1. Field of the Invention
The present invention relates to an optical disk drive, and more particularly to a circuit for detecting the mirror signal used for counting the number of the tracks of the optical disk jumped, and a method therefore. The present application is based on Korean Patent Application No. 98-55901, which is incorporated herein by reference.
2. Description of the Related Art
The mirror signal is generated when the pickup of an optical disk drive jumps from one track of a disk to another, and is used to count the number of the tracks jumped. It is very important for the pickup to correctly jump a desired number of tracks since the performance of the optical disk drive depends on the speed of searching a data position targeted on the disk. Such mirror signal is detected by a mirror circuit connected with a RF (radio frequency) amplifier.
Referring to FIG. 1, the data recorded on the optical disk 2 is picked up by the pickup 4 to generate data signals amplified by the RF amplifier 6. A part of the data signals is applied to the mirror circuit 8 to perform the bottom hold and peak hold. Conventionally, the peak hold is a tracking signal of 30 KHz set by a time constant to be tracked down, while the bottom hold is set by a time constant for the fluctuation of the envelope to be tracked down in a cycle.
FIG. 2 is a block diagram for illustrating an example of the conventional mirror circuit, FIG. 3 the waveforms generated by the circuit of FIG. 2 with a constant DC level of the input signal, and FIG. 4 the waveforms with a rapidly fluctuated DC level of the input signal. The operation of the mirror circuit is described as follows:
First, the input signal Vin from the RF amplifier 6 is delivered to a first peak hold circuit 10 to hold the peak value, and to a first bottom hold circuit 12 to hold the bottom value. The difference between the peak and the bottom value is amplified by a differential amplifier 14 to generate a waveform as indicated by reference symbol xe2x80x9caxe2x80x9d in FIG. 3. The differential amplifier is connected with a logic circuit for detecting the centered value, which comprises a second peak hold circuit 16, second bottom hold circuit 18, resistors 20, 22, and buffer 26. The amplified signal xe2x80x9caxe2x80x9d of the differential amplifier is delivered to both the second peak and bottom hold circuits 16 and 18 to respectively hold the peak value xe2x80x9cbxe2x80x9d and the bottom value xe2x80x9ccxe2x80x9d as shown in FIG. 3. The output of the second peak hold circuit 16 is connected through the resistor of resistance xe2x80x9cRxe2x80x9d to a node 24, while the output of the bottom hold circuit 18 is connected through the resistor of same resistance xe2x80x9cRxe2x80x9d to the node 24. The node 24 is also connected to the non-inverted input (+) of the buffer 26, so that the output of the buffer 26 has the value xe2x80x9cdxe2x80x9d centered between the peak value xe2x80x9cbxe2x80x9d and the bottom value xe2x80x9ccxe2x80x9d. The centered value xe2x80x9cdxe2x80x9d is applied to the non-inverted input (+) of a comparator 28, which compares it with the output value xe2x80x9caxe2x80x9d of the differential amplifier 14 received through the inverted input (xe2x88x92) to generate a mirror signal.
In this case, if the input signal Vin from the RF amplifier 6 has a constant DC level, the mirror signal has the normal waveform as shown in FIG. 3. However, if the DC level of the input signal Vin is abruptly changed due to a certain cause, the mirror signal has an abnormal waveform as shown in FIG. 4, because it is impossible to correctly detect the centered value xe2x80x9cdxe2x80x9d between the peak and bottom values. Namely, the mirror signal includes such error as indicated by reference numeral 100 in FIG. 4. The cause of abruptly changing the DC level of the input signal Vin may be a wobble signal loaded on the disk as in CD-RW (Compact Disk-ReWritable) or DVD-RAM (Digital Versatile Disk-Random Access Memory), or a header signal inputted in case of CD or DVD, or a defect existing in the disk. The header signal inherently has a greater DC level than the data signal.
More specifically, the second peak hold circuit 16 as shown in FIG. 2 correctly detects the peak value xe2x80x9cbxe2x80x9d due to the relatively rapid charging time constant when the input signal from the RF amplifier 6 has an abruptly increasing DC value, but cannot correctly detect the peak value xe2x80x9cbxe2x80x9d due to the relatively slow discharging time constant when the DC value abruptly decreases. On the contrary, the second bottom hold circuit 18 cannot correctly detect the bottom value xe2x80x9ccxe2x80x9d due to the relatively slow charging time constant when the DC value of the input signal abruptly increases, but correctly detects the bottom value xe2x80x9ccxe2x80x9d due to the relatively rapid discharging time constant when the DC value rapidly decreases. Accordingly, the mirror circuit generates the centered value xe2x80x9cdxe2x80x9d of the abnormal waveform when the DC value of the input signal rapidly increases, so that the error 100 is generated in the mirror signal MIRROR, as shown in FIG. 4.
It is an object of the present invention to provide a circuit for correctly detecting the mirror signal regardless of variation of the DC level of the input signal that is picked up from a disk of an optical disk drive, and then amplified by the RF amplifier, and a method therefore.
It is another object of the present invention to provide an optical disk drive with a circuit for correctly detecting the centered value of the input signal rapidly changing during detection of the mirror signal.
According to an aspect of the present invention, a circuit for detecting the mirror signal from the output signal of an RF (radio frequency) amplifier for amplifying the signal picked up from a disk of an optical disk drive with a radio frequency, comprises a first peak hold circuit for holding the peak value of the output signal of the RF amplifier to provide a first peak value, a first bottom hold circuit for holding the bottom value of the output signal of the RF amplifier to provide a first bottom value, a differential amplifier for amplifying the difference between the first and second peak values, a second peak hold circuit for holding the peak value of the output signal of the differential amplifier to provide a second peak value, a second bottom hold circuit for holding the bottom value of the output signal of the differential amplifier to provide a second bottom value, a centered value extractor for processing the second peak and bottom values to extract the centered value of the output signal of the RE amplifier, a comparator for comparing the centered value with the output signal of the differential amplifier to generate the mirror signal, and a hold time constant adjustment circuit connected between the centered value extractor and the second peak and bottom hold circuits to adjust the time constants of the second peak and bottom hold circuits according to a change of the level of the output signal of the RF amplifier.
According to another aspect of the present invention, a method of detecting the mirror signal used for counting the number of tracks of a disk jumped by the pickup of an optical disk drive, comprises the steps of detecting the difference between the peak and bottom values of a whole signal read by the pickup during the jumping so as to generate a differential signal, obtaining the centered value between the peak and bottom values of the differential signal, adjusting the charging and discharging time constants used for detection of the peak and bottom values of the differential signal according to the variation between the peak and bottom values of the differential signal, and comparing the differential signal with the centered value according to the variation of the charging and discharging time constants so as to generate the mirror signal.
According to still another aspect of the present invention, an optical disk drive comprises an optical disk, a pickup for reading data recorded on the optical disk to generate a whole signal, a mirror signal detector for detecting the difference between the peak and bottom values of the whole signal to generate a differential signal, obtaining the centered value between the peak and bottom values of the differential signal, adjusting the charging and discharging time constants used for detection of the peak and bottom values of the differential signal according to variation between the peak and bottom values of the differential signal, and comparing the centered value according to variation of the charging and discharging time constants with the differential signal so as to generate the mirror signal, and a servo controller for counting the number of the tracks jumped by the pickup according to the mirror signal to move the pickup to a targeted track.
The present invention will now be described more specifically with reference to the drawings attached only by way of example.